The smell of wet earth after rain is called petrichor.
Why it is true
Petrichor is caused by a mixture of compounds, including geosmin, produced by soil bacteria, and ozone brought by the rain. The smell is more intense after a dry period, when the drops hit dry soil.
Source: Nature
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.